Quantum theory of molecular collisions in a magnetic field: Efficient calculations based on the total angular momentum representation

Abstract

An efficient method is presented for rigorous quantum calculations of atom-molecule and molecule-molecule collisions in a magnetic field. The method is based on the expansion of the wave function of the collision complex in basis functions with well-defined total angular momentum in the body-fixed coordinate frame. We outline the general theory of the method for collisions of diatomic molecules in the 2 and 3 electronic states with structureless atoms and with unlike 2 and 3 molecules. The cross sections for elastic scattering and Zeeman relaxation in low-temperature collisions of CaH (+ 2) and NH (- 3) molecules with H3 e atoms converge quickly with respect to the number of total angular momentum states included in the basis set, leading to a dramatic (>10-fold) enhancement in computational efficiency compared to the previously used methods [A. Volpi and J. L. Bohn, Phys. Rev. A 65, 052712 (2002); R. V. Krems and A. Dalgarno, J. Chem. Phys. 120, 2296 (2004)]. Our approach is thus well suited for theoretical studies of strongly anisotropic molecular collisions in the presence of external electromagnetic fields. © 2010 American Institute of Physics.